What Is Ionic Polymerization?


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In ionic polymerization, the activator is not a radical but an ion. Similar to radical polymerization, ionic polymerization is also a chain reaction. In the polymerization of styrene with tetrahydrofuran as the solvent and cumyl potassium as the initiator, the latter dissociates into a positive potassium ion and a negative cumyl ion.

The potassium ion is solvated in tetrahydrofuran. The cumyl ion opens the styrene double bond and attaches itself to one end of the carbon-carbon bond and the excess electrons are pushed to the other end of the carbon-carbon bond thus forming a new anion which can grow by adding \other monomers. This is an example of anionic polymerization.

During changing growth, monomers continue to add to the anionic chain end so that the chain grows by two C-atoms at a time. In both anionic and cationic polymerization, there is no termination through combination of two chains because the ionic chain ends, which have the charge, would repel each other. Termination takes place by the addition of water, alcohol, acids or amines. With out such additions the chains keep growing until the monomer is exhausted and the reaction stops. This type of reaction is known as living polymerization reaction.

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